Conventional hydride-based batteries provide a low-cost energy system. However, the energy density of these batteries can be relatively low. For example, state-of-the-art metal hydride batteries can provide an energy density of approximately of 60 Whr/kg.
Conventional nickel-metal hydride (MH) batteries include a positive electrode containing nickel hydroxide, a negative electrode containing a metal hydride, a separator between the positive and negative electrodes and an alkaline electrolyte. The electrolyte commonly includes an aqueous solution of potassium hydroxide. Charge and discharge reactions for nickel metal hydride batteries may be written as:Positive electrode: Ni(OH)2+OH−→NiOOH+H2O+e−(charge)  (1)NiOOH+H2O+e−→Ni(OH)2+OH (discharge)  (2)Negative electrode: M+H2O+e−→MHab+OH− (charge)  (3)MHab+OH−→M+H2O+e− (discharge)  (4)Where M is a hydrogen absorbing alloy and Hab is absorbed hydrogen.
Conventional separator materials for metal hydride batteries include woven or nonwoven fabrics of polymer fibers such as polyamide, polyolefin and nylon. Porous polymeric films are also used. U.S. Pat. No. 8,012,621 describes separators of alkali ion conductive solid electrolytes including solid Me SICON (Metal Super Ion CONducting material). U.S. Pat. No. 8,012,621 also describes alkali ion conducting, substantially nonporous polymer separators which include cation exchange membrane material made of a polymer with fixed anionic functional groups attached to a polymer backbone and alkali metal cations as mobile species.